情态确认型“是”字构式中“是”的语义功能

“是”从代词演变为断定系词，进而成为焦点标记，是语法界普遍接受的事实。而且，“是”还可以用在小句开头形成“是S”构式，以及某些副词、连词之后形成“X是”构式。这两种构式可以分别称为“是认”型和“断定悬空”型，这是“是”的情态功能，即表达说话人的主观断定。语法化研究者着力于形式方面的特点，语义分析则告诉我们，两种型式下的“是”既有差别，又有联系：“是认”型中的“是”一般不可省缺，“断定悬空”型中的“是”可省。“是”可否缺省的语义基础是“是”在其所在结构中的辖域关系。

Semantic function of Shi in Modally identifying construction

It is generally accepted that Shi evolved from a pronoun to a assertive copular and to a focus marker. Stepping further, Shi may occur before some clauses resulting in 'Shi S' construction and before some adverbs and conjuncts forming 'X Shi' construction called 'identifying' token and 'suspending assertion' token respectively. These two constructions embody the modal function of Shi, that is, the function to express speaker's subjective assertion. Those who study grammaticalization only have eyes for formal features. Analysis of meaning shows that the 'Shi' in two tokens have differences and connections as well. The first token generally has 'Shi' and the second one may omit it, depending upon the relation of semantic scope.